1. Field of the Invention
This invention relates to a control device for a three-phase brushless motor.
2. Description of the Related Art
A three-phase brushless motor has a plurality of stator coils arranged around a rotor which is configured of permanent magnets. The number N of the stator coils is equal to the number of slots between the respectively adjacent stator coils, and it is also called the “slot number”. A switch circuit for switching energizations is connected to the N stator coils. The switch circuit switches the energizations for the respective stator coils in accordance with the rotation of the rotor. This switch circuit changes-over energization switching timings for the N stator coils, on the basis of position detection signals which a position detection signal generation device generates. The position detection signal generation device includes three position sensors, and the position detection signals are successively generated in correspondence with the rotational positions of the rotor by the three position sensors.
In a case where errors have developed in the mounting positions of the three position sensors, positional deviations occur in the position detection signals. Besides, in a case where errors have developed in the magnetized positions of the rotor or a position detecting rotor, positional deviations similarly occur in the position detection signals. The positional deviations of the position detection signals afford deviations to the energization switching timings of the stator coils based on the switch circuit, they incur unnecessary rotational frequency fluctuations in the three-phase brushless motor, and they afford unnecessary demagnetizations to the rotor.
Patent Document JP2002-199775A discloses a prior-art technique wherein an EEPROM is disposed in a control device for a three-phase brushless motor, and timing data which stipulate the switch timings of a switch circuit in correspondence with the errors of the mounting positions of position sensors are stored in the EEPROM. With the prior-art technique, the timing data stored in the EEPROM are adjusted, thereby to adjust the energization switching timings of stator coils and to exclude the errors of the mounting positions of the position sensors.
In the prior-art technique disclosed in Patent Document, however, complicated adjustments are required for the adjustments of the timing data recorded in the EEPROM, and a productivity lowers. Besides, since the timing data correspond to the errors of the mounting positions of the position sensors, they cannot cope with the case where the errors have developed in the magnetized positions of the rotor or the position detecting rotor.